I have built a prototype Arduino shield/Arduino derivative board thing, but before I produce a final release version I have been wondering the following.
When providing 0.1" headers for I/O on the board, what pin layout order should I use for GND, 5V and signal? I cannot seem to find a standard described anywhere. If I look through my collection of Arduino boards and accessories, I find most are GND, 5V, then signal, but not always. Some are GND, signal, then 5V. If there is a proper standard I'd like to follow it for the board I'm designing. I'd like to think that if there is a standard (say) temperature sensor out there with 3-pin plug, that my board would accept it (rather than blow it up!).
I'm planning on using the commonly available keyed Molex KK headers 0.1" pitch. Same as the Tinkerkit http://store.arduino.cc/ww/index.php?main_page=product_info&cPath=16&products_id=253 (http://store.arduino.cc/ww/index.php?main_page=product_info&cPath=16&products_id=253) and http://store.arduino.cc/ww/index.php?main_page=product_info&cPath=16&products_id=119 (http://store.arduino.cc/ww/index.php?main_page=product_info&cPath=16&products_id=119). Incidentally Tinkerkit have Signal on the middle pin.
A secondary question that arises - which signal should be on pin 1? Some of my Arduinos are pin 1 = GND, others pin 1 = 5V. This of course only matters with keyed headers as an un-keyed varieties can be plugged in either way round (the right way and the likely terminally-kill-the-part way).
Perhaps since there doesn't appear to be a clear dominating standard I should instead assume no standard and just do it the way I choose?
I am not aware of a standard for such a thing but it would be good to be pin compatible with sensors arduino store sells.
Yeah, in the absence of any other ideas I think I'll follow what has been done with Tinkerkit to make things mix and match. I think I'll make my four pin 1-WIRE connector the same pin out as Tinkerkit too.
What I am thinking is a 5-wire connector with symmetric pins say 5V-out-gnd-out-5V so even if you plug in wrong it will still work :) Just a thought, like apple's new connector.
Well I've decided to go with the defacto standard that a lot of sensors use. That is, the ordering GND, VCC, SIGNAL. The advantage of this is that if people use a bare header on my board they can plug in directly a defacto standard sensor. If people decide to use a keyed KK header instead (the silk screen will have the drawing of a keyed KK header) then they will have all the advantages of a connector that doesn't easily get knocked out. In this case, the pin out will be 1-GND, 2-VCC, 3-SIGNAL. This is not compatible with the Tinkerkit, but as I dig deeper it looks like the Tinkerkit gear, at least at this point in time, really isn't that popular and so not much to be gained from a pin out that would not be as flexible as the one I've decided upon.
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